1. Field of the Invention
This invention relates to technology for printing an image by forming dots on a print medium.
2. Description of the Related Art
As output devices for images created using a computer or images shot using a digital camera or the like, printing devices that print images by forming dots on a printing medium are widely used. These printing devices perform gradation expression using a halftone process because there are few dot tone values that can be formed for the input tone values. As one halftone process, an ordered dither method using a dither matrix is widely used. The ordered dither method has a big effect on the image quality according to the dither matrix contents, so for example as disclosed in JP-A-7-177351, JP-A-7-81190, and JP-A-10-329381, an attempt was made to optimize the dither matrix using an analysis method of simulated annealing or genetic algorithm using an evaluation function taking into consideration the human visual sense.
However, with this kind of dither matrix optimization process, ink dots are formed by doing a plurality of scans of a common area on the printing medium, and there was no consideration of the degradation of the image quality due to printing of the images in this way. Furthermore, this kind of image quality degradation is not limited to halftone processing using the dither matrix, but also generally occurred with printing using halftone processing with the error diffusion method or other methods.